The effect of kefir and peppermint extract (Mentha pipperita) extract in drinking water on performance, lipid profiles, thyroid hormones and testosterone hormone of Japanese quail

Introduction: Application of antibiotics causes two major health problems, including antibiotic residues in body tissues and animal products and the resistance of pathogens to antibiotics. On the other hand, antibiotics improve growth, feed efficiency and control infectious diseases. Following the ban on the use of antibiotics as growth stimulants in the poultry industry, the EU has been paying more attention to non-antibiotic growth-promoting compounds since 2006, including organic acids, probiotics and herbs. Previous studies have shown that in many oils of dark plants Mentha pipperita, thymol, carvacrol, menthol and in some cases paracetamol are the most important components of growth improvement, their antimicrobial and antioxidant properties. kefir is also a natural probiotic. The fermenting agent of kefir milk is kefir seeds, which contain casein and the species Lactobacillus, Saccharomyces, Streptococcus and others. Diets containing Mentha pipperita, by improving the microflora of the gastrointestinal tract and reducing the population of harmful microbes, can create better conditions for the use of final feed products and thus improve the growth and better performance of chickens. In studies, the positive effects of kefir on the performance and biochemical parameters of broiler blood have been reported.Materials and Methods: This study was conducted in the animal husbandry research station of Khuzestan University of Agriculture and Natural Resources. In this study, four hundred one-day-old Japanese quails were used in a completely randomized design with four treatments, four replications and 25 observations per replication for 35 days. The experiment was performed. Treatments are: Treatment 1) Basic diet + drinking water (control group), Treatment 2) Basic diet + drinking water + 0.5% Mentha pipperita extract, Treatment 3) Basic diet + drinking water + kefir milk 2%, Treatment 4) Basic diet + drinking water + Mentha pipperita extract 0.5% + kefir milk are 2%. The weight of quails was measured at the end of each week and the feed consumed was determined. The average of daily weight gain, feed intake and feed conversion ratio were calculated. At the end of the fifth week, from each replicate, two quails with a weight close to the average were selected and slaughtered.  Breast and thigh meat samples were used to measure pH, water holding capacity and meat moisture content. Also, at the end of the fifth week, two samples were randomly selected from each replicate and blood was taken from their wing vein to measure blood parameters, thyroid hormones and testosterone.Results and Discussion: The addition of mint and kefir extract significantly increased the weight of Japanese quails. The highest weight gain in the third and fourth weeks was observed in treatments 2, 3 and 4, respectively. In a study that investigated the effect of kefir on broiler performance, it was shown that the use of kefir as a natural probiotic causes significant weight gain, which is consistent with the present results. Mentha pipperita essential oil and kefir have been reported to improve feed conversion ratio and stimulate digestion in broilers. Kefir added to broiler drinking water has been reported to increase body weight, increase daily weight, reduce daily feed intake and feed conversion ratio, and improve performance. Mentha pipperita lowers blood cholesterol levels by liver or intestinal cells. Peppermint also accelerates LDL catabolism by increasing liver LDL receptors. In addition, Mentha pipperita inhibits the activity of the enzyme fatty acid synthase (FAS) and increases the beta oxidation of fatty acids, thereby effectively reducing fat storage. The concentration of thyroid hormones was not affected by the treatments. In some studies, thyroid hormone concentrations increase with nutrition of mint and kefir. Testosterone concentrations were significantly affected by experimental treatments. Changes in the hypothalamic-pituitary-gonadal axis are the most important factors affecting the reproductive system. So far, the effect of many different plant extracts on the hypothalamic-pituitary-gonadal hormonal axis has been investigated. Plant extracts such as marjoram and ginger have been reported to increase testosterone, LH and sometimes FSH, and play an effective role in activating the hypothalamic-pituitary-gonadal axis. Peppermint, with its special chemical composition, can stimulate the signaling pathways of sex steroid production in the hypothalamic-pituitary-gonadal axis. The effect of experimental treatments on pH and moisture of breast and thigh meat and their water holding capacity was not significant.Conclusion: According to this study and economic considerations, it seems that the combined use of 2% kefir and 0.5% Mentha pipperita in drinking water can improve the performance and also modulate lipid profiles in Japanese quails, as well as increase reproductive performance in males.